The present invention relates to radio frequency (RF) power amplifiers.
Wireless communication devices such as laptop personal computers, personal digital assistants, mobile internet and email devices, cellular phones, smart phones, and wireless household appliances are being developed in ever increasing functions supported by expanded circuit features. Correspondingly, electrical components thereof must decrease in size while still providing radio transmission performance. A major component of a wireless communication device is the power amplifiers. A power amplifier can be fabricated in an integrated circuit to provide signal amplification with substantial power. For high order modulated signals used in high speed wireless data, a significant challenge to the RF power amplifiers is to provide high linearity power amplification while minimizing power consumption to extend the time between consecutive battery charges in the mobile wireless devices. Another requirement for mobile wireless devices is to reduce heat dissipation to allow the proper operation of the electronic circuits in the wireless devices.
A recent development in high speed wireless communication technologies is the use of multiple-input multiple-output communications (MIMO), which is adopted as a key component in the high speed wireless standards such WiMax, LTE, LTE-Advanced, or other 4G wireless standards. MIMO refers to the technology where there are multiple antennas at the base station and multiple antennas at the mobile wireless device. Examples of a multiple antenna technology includes cellular phones with two antennas, laptops with two antennas (e.g. built in the left and right side of the screen), as well as customer-premises equipment (CPE) wireless devices with multiple sprouting antennas. MIMO can enable space-time code or spatial multiplexing in which two or more antennas can be employed at the transmitter. When two or more antennas are used in RF signal transmitting, two or more power amplifiers are generally needed.
There is therefore a need for more energy efficient RF power amplifiers to enable newly developed high speed wireless communication technologies.